In recent years, internal combustion engines provided with devices for controlling the operating angles, valve lifts, and other valve operating characteristics of the intake valves and exhaust valves in addition to the throttle valves and controlling the valve operating characteristics along with the throttle valve opening degrees so as to control the amounts of air taken into the combustion chambers (hereinafter “intakes”) have been developed and become known.
On the other hand, in the past, in multicylinder internal combustion engines, due to assembly tolerances and mechanical tolerances of the valve parts or wear or deposits of the valve parts, variations arise in the intakes of the cylinders resulting in the problems of torque fluctuations and deteriorated exhaust emissions. Such problems similarly occur sometimes even in multicylinder internal combustion engines of types controlling the valve operating characteristics to control the intakes. It has been learned that in the case of the same intake pressure, the effect becomes greater the less the intake caused by the valve operating characteristics, that is, the smaller the operating angle or valve lift of an intake valve.
More specifically, assuming for example the same amount of deposit sticking to an intake valve, with respect to the same target intake, the deviation of the actual intake from the target intake becomes greater in the case of intake reducing the operating angle or valve lift compared with the case of intake increasing the operating angle or valve lift. As a result, the effect on the torque fluctuation etc. becomes greater the smaller the operating angle or the valve lift.
To deal with this problem, Japanese Unexamined Patent Publication (Kokai) No. 2002-303187 discloses a multicylinder internal combustion engine of the type controlling the valve operating characteristics to control the intake wherein the torque difference of cylinders is found and the fuel injection amount or ignition timing for each cylinder is corrected so as to reduce the torque difference of the cylinders. Further, this publication discloses to set the correction amount of the fuel injection amount etc. larger the smaller the operating angle of an intake valve so as to deal with the fact that the deviation between the actual intake and the target intake becomes greater the smaller the operating angle of an intake valve.
Further, Japanese Unexamined Patent Publication (Kokai) No. 2001-173469 discloses a variable valve device of an internal combustion engine provided with an actuation mechanism able to change the valve lift wherein since the intake difference of cylinders appears remarkably in a region where the valve lift is extremely small (superlow lift control region), this superlow lift control region is not used.